When a downhole tool, such as a packer or liner hanger, is run downhole, fluid and debris traveling past the tool can sometimes move the tool's slips outward, potentially damaging the slips, hindering the tool's deployment, or affecting the function of the slips once the tool is set at depth.
In FIG. 1, for example, a slip 20 is positioned on a tool housing or mandrel 10 between a movable wedge 12 and another (fixed or movable) wedge 14. When the tool mandrel 10 is set at depth, activation of the tool moves the wedges 12 and 14 closer together to push the slip away from the mandrel 10 so it can engage the inside of a surrounding tubular. To retain the slip 20 during deployment, a plurality of rings 30 fit through the slip 20 and around the mandrel 10. When the wedges 12/14 are separated as shown, the rings 30 hold the slip 20 next to the mandrel 10 so that the slip 20 does not extend beyond the tool's profile. When pushed out from the mandrel 10, however, the slip 20 overcomes the hold of the rings 30.
In addition to rings, other features such as springs, shear pins, and cages may be used to retain the slips in place until the tool is set at its desired depth. For example, a bow or leaf spring 32 can be positioned in FIG. 1 between the cage 16 and the slip 20 to bias the slip 20 against the mandrel 10. Although some of these features can retain the slip 20 while the tool is both run-in and pulled-out-of the hole, retaining the slips 20 with some of these features can be used only for running-in hole. For example, a shear pin may no longer be used to retain the slip once broken. Therefore, problems with debris and fluid passing around the unretained slip may occur as the tool is pulled out of the hole.
Although shown in a diagrammatic fashion in FIG. 1, use of the rings 30 (as well as other features such as springs, pins, and the like) to mechanically retain the slips 20 typical requires some mechanical complexity to achieve the desired retention on an actual tool. The mechanical complexity makes manufacture and assembly of a tool more involved and expensive, and can lead to a higher potential for mechanical failure in the tool. What is needed is a technique to retain slips on a downhole tool that requires less complexity and that can be effective as the tool is run-in and pulled-out-of a hole.